Control system for a failure mode testing system

ABSTRACT

A control system for a failure mode testing system is described. The control system employs at least one control algorithm that enables the testing system to be operated at optimal pressure and frequency levels in order to generate a desired system response, such as a desired energy level and desired slope of the fast Fourier transform of the system response. Also described are a pressure dither system and a frequency ringing system for enhancing the operation of the actuator cylinders of the failure mode testing system. All three of the systems can be incorporated, either singularly or in combination, into a computer software program that can be employed to operate and control the failure mode testing system.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part application of U.S.patent application Ser. No. 09/316,574 entitled “Design MaturityAlgorithm”, filed May 21, 1999, pending, which is a continuation-in-partapplication of U.S. patent application Ser. No. 08/929,839 entitled“Method and Apparatus For Optimizing the Design of Products”, filed Sep.15, 1997, pending, the entire specifications of which are expresslyincorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to a new and improved controlsystem for a failure mode testing system. The control systems employs atleast one control algorithm in order to optimize the performance of thefailure mode testing system.

BACKGROUND OF THE INVENTION

[0003] The recent advent of failure mode testing systems to activatefailure modes has enabled manufacturers to discover latent defects orflaws which may eventually lead to the failure of a product, componentor sub-component. The methodology of these testing systems generallyinvolves the application of one or more types and/or levels of stimulito the product, component or sub-component until one or more failuremodes are activated. Typically, one of the stimuli includes vibration,such as that caused by striking a piston, rod, or other suitable device,against the product, component or sub-component itself, or a surface incontact with the product, component or sub-component. When the failuremode is activated, the failed product, component or sub-component isthen either repaired, replaced, or redesigned. This process may then berepeated in order to activate and eliminate other failure modes.

[0004] A proprietary testing system has been developed by Entela, Inc.(Grand Rapids, Mich.) and is referred to as a failure mode verificationtesting system. This system, which is described in commonly-owned,co-pending U.S. patent application Ser. No. 09/316,574 entitled “DesignMaturity Algorithm”, filed May 21, 1999, and U.S. patent applicationSer. No. 08/929,839 entitled “Method and Apparatus For Optimizing theDesign of Products”, filed Sep. 15, 1997, employs an apparatus which iscapable of generating a wide variety of stress patterns, especially sixaxis uniform random stress patterns, in a product, component, orsub-component in order to activate the failure modes of that particularproduct, component, or sub-component.

[0005] A six axis uniform random stress is generally defined as thestress history at a point having uniform random distribution with thestress being comprised of tension and compression stress in threeorthogonal axes and torsion stress about the same three orthogonal axes.Six axis uniform random stress patterns are generally defined as sixaxis uniform random stress at all points on a product such that thestress history of the six axis uniform random stress at each point formsa time history of non-repeating stress patterns.

[0006] The apparatus uses six axis uniform random actuation at one ormore mounting locations of a product to produce six axis uniform randomstress patterns in the product. These six axis uniform random stresspatterns identify failure modes previously uncovered with other testingmethodologies. Furthermore, the simultaneous introduction of otherstimuli (at varying levels), such as temperature, vibration, pressure,ultraviolet radiation, chemical exposure, humidity, mechanical cycling,and mechanical loading, identify other failure modes associated with theproduct.

[0007] In order to create the six axis uniform random stress patterns inthe product, the apparatus employs a plurality (preferably six) ofactuators, also referred to as force imparting members, that can beoperated either pneumatically, hydraulically, by a combination of bothpneumatic and hydraulic power, or any other force imparting mechanism. Aportion of the actuators, such as the cylinders, are typically mounted(including slidingly), either directly or indirectly, onto one or moresupport members.

[0008] If six actuators are being used, they are preferably arranged inpairs, each pair being set about 120 degrees apart from the other pair.Each actuator is simply comprised of a cylinder acting in cooperationwith a piston in order to produce force and torque upon a point ofrotation. The pressure to each actuator is preferably cycled betweenmaximum extend pressure and maximum retract pressure in a linear“saw-tooth” manner. The frequency for each actuator is slightlydifferent. This difference in frequency causes an interference patternof the cycling as the actuators come in and out of phase with eachother. It is this difference in the frequencies of the actuators whichcreates a six axis uniform random stress in the product. By way of anon-limiting example, the six pneumatic actuators can be operated atfrequencies of 1.8 Hz, 1.9 Hz, 2.0 Hz, 2.1 Hz, 2.2 Hz, 2.3 Hz, and 2.4Hz, respectively. Therefore, as the actuators come in and out of phasewith one another, the frequency content in the center will go from about2 Hz to infinity. It should be noted that other frequencies may be usedfor the individual actuators in order to produce an even lowerfrequency.

[0009] A portion of the actuators, such as the pistons, are typicallyconnected, either directly or indirectly, to a platform, such as a hub,upon which the product is mounted. As the actuators are actuated, theyproduce a force which generates a torque about a point of rotation onthe platform. It should be noted that whether a torque is generatedabout the point of rotation will depend upon which actuators are beingactuated and in what sequence with respect to one another. The force andtorque are eventually transferred from the platform to the productitself, thus creating the six axis uniform random stress patterns in theproduct.

[0010] During routine operation of the apparatus, it is not uncommon forthe actuators to be cycled back and forth very rapidly. Therefore, it isimpractical to manually attempt to continuously adjust the variousoperational parameters that affect actuator operation, such as thepressure and frequency of the cylinders. The pressure parameter concernsthe amount of pressure in the air line (e.g., in a pneumatic system) incommunication with the cylinder of the actuator, which is typicallyexpressed in pounds per square inch (psi). The frequency parameterconcerns the frequency that each cylinder is set to, which is typicallyexpressed in Hertz (Hz).

[0011] By way of a non-limiting example, the system response of theapparatus can be measured in terms of energy E (e.g., grms or peak G)and slope m of the fast Fourier transform (FFT) of the system response.A FFT is typically performed on a time history or a response. By way ofa non-limiting example, an acceleration signal from an accelerometerwould provide a varying signal in time. The FFT of the accelerationsignal would give the acceleration level vs. frequency. From the FFT ofthe acceleration signal, the slope of the FFT plot (i.e., response levelvs. frequency) can be determined.

[0012] Preferably, a desired energy level E having a desired slope m(e.g., flat) is produced by the application of appropriate levels ofpressure and frequency. For example, if the energy level were plotted onthe Y-axis of a graph and the frequency level were plotted on the X-axisof that same graph, the majority of data points could be bisected by aline having a slope substantially equal to zero. Thus, the energy levelwould be substantially constant over the entire frequency range.

[0013] Due to the large number of calculations that would have to beperformed on a split second basis for each of the six actuators, it isimpractical to manually perform the calculations, let alone make therequisite adjustments to the operational parameters of the actuators,without adversely affecting the efficient performance of the testingsystem. Nonetheless, it is important to the optimal operation of thetesting system that the desired performance parameters are achieved andmaintained during the course of the testing procedure.

[0014] Additionally, with respect to pressure, it has been observed thatby keeping each cylinder at a constant pressure, the actuators have atendency, due to frictional forces and historesis, to gravitate towardsa set point and get stuck, thus causing the actuators to improperlyfunction. For example, if the pressure is slightly too high, theapparatus will tend to drift up and then get stuck. Conversely, if thepressure is slightly too low, the apparatus will tend to drift down andthen get stuck.

[0015] Furthermore, with respect to frequency, it has been observed thatby keeping each cylinder at a specific individual frequency, over timeone of the actuators will receive less energy than the other actuators.For example, if one cylinder of an actuator pair is operated at 5 Hz ata given pressure, and the other cylinder of the actuator pair isoperated at 5.5 at that same given pressure, then over time a littlemore energy is being given to one cylinder than the other. The fact thatone cylinder receives more energy can be confirmed by calculating theintegration of the given pressure at the slightly higher frequency. As aresult, the apparatus will tend to drift toward the actuator having thelowest energy level, thus causing performance problems.

[0016] Therefore, there exists a need for a control system fordetermining if the desired system response of a failure mode testingsystem is or is not present. The control system should be capable ofquickly, accurately, and if needed, constantly adjusting the operationalparameters (e.g., pressure and frequency) until the desired systemresponse is achieved and subsequently maintained.

SUMMARY OF THE INVENTION

[0017] General objects of the present invention are to facilitate andenhance testing of products under various conditions, to provide morecomprehensive testing and to make testing more efficient by reducing theenergy, time, and expense required to undertake testing.

[0018] Another object of the present invention is to provide a new andimproved control system for a failure mode testing system.

[0019] Still another object of the present invention is to provide a newand improved control algorithm for a failure mode testing system.

[0020] In accordance with one embodiment of the present invention, acontrol system for a failure mode testing system having a determinablesystem response is provided, wherein the testing system includes aplurality of actuator cylinders, each cylinder operating at an initialpressure and an initial frequency, wherein the frequency of each of thecylinders is different, comprising:

[0021] a) selecting a desired system response;

[0022] b) determining the system response;

[0023] c) determining whether the desired system response is present;and

[0024] d) changing an operational parameter of the cylinders by asufficient amount in order to achieve the desired system response,wherein the operational parameter is selected from the group consistingof pressure, frequency, and combinations thereof.

[0025] A more complete appreciation of the present invention and itsscope can be obtained from understanding the accompanying drawings,which are briefly summarized below, the followed detailed description ofthe invention, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a schematic of a control system for a failure modetesting system, in accordance with one aspect of the present invention;

[0027]FIG. 2 is a schematic of a pressure dither system for a failuremode testing system, in accordance with one aspect of the presentinvention;.

[0028]FIG. 3 is a schematic of a frequency ringing system for a failuremode testing system, in accordance with one aspect of the presentinvention;

[0029]FIG. 4 is a schematic of a computer software program for a controlsystem for a failure mode testing system, in accordance with one aspectof the present invention; and

[0030]FIG. 5 is a schematic of an alternative computer software programfor a control system for a failure mode testing system, in accordancewith one aspect of the present invention.

[0031] The same reference numerals refer to the same parts throughoutthe various Figures.

DETAILED DESCRIPTION OF THE INVENTION

[0032] In accordance with one embodiment of the present invention, acontrol system employing at least one control algorithm is provided foruse in conjunction with a failure mode testing system. The controlalgorithm enables the testing system to be operated at optimal pressureand frequency levels in order to generate a desired system response. Thecontrol algorithm can be incorporated into a computer software programthat can be employed to control and operate the failure mode testingsystem (e.g., a control system).

[0033] The control algorithm of the present invention is actuallycomprised of a number of discrete algorithms, each of which generallydetermine a single piece of information, based on data provided byvarious input sources, such as sensors, detectors, data storage mediums,and so forth.

[0034] By way of a non-limiting example, one set of algorithmsdetermines the change in energy due to pressure, the change in energydue to frequency, the change in slope due to pressure, and the change inslope due to frequency. That information is then utilized by additionalalgorithms to determine the average energy and slope of the systemresponse. That information is then utilized by still additionalalgorithms to determine the new target energy and slope of the systemresponse. Finally, that information is utilized by still yet another setof algorithms to determine the new target frequency and pressure toachieve the new target energy and slope of the system response.

[0035] With reference to FIG. 1, there is illustrated a schematic viewof a non-limiting example of a control system employing at least onecontrol algorithm, in accordance with one embodiment of the presentinvention. The control algorithm is intended to be used in conjunctionwith a failure mode testing system employing an apparatus that iscapable of producing six axis uniform random stress patterns in aproduct.

[0036] As shown in condition box 10, and by way of a non-limitingexample, the actuators of the apparatus are assigned a pre-selecteddefault pressure (P) and a pre-selected default frequency (F). Thesepre-selected defaults are set by the operator, and, of course, it shouldbe noted that they may be changed or altered to meet the desiredoperational parameters of the testing system. Additionally, the pressurechange (dp) is set at 10 psi (although any other figure may besubstituted therefor), the frequency change (df) is set at 0.5 Hz(although any other figure may be substituted therefor), and the stepfrequency (f) is set at 0.2 Hz (although any other figure may besubstituted therefor).

[0037] As shown in box 20, and by way of a non-limiting example, thepressure of the actuator cylinder is set to P+dp. Each of the actuatorcylinders are set to different frequencies, F1, F2, F3, F4, F5, and F6,respectively. F1 is equal to F+f+df. The step frequency (f) is used to“step” the base frequency up to six distinct frequencies, i.e. adifferent frequency for each cylinder, as will become apparent from thefollowing description. F2 is equal to F+2f+df, F3 is equal to F+3f+df,F4 is equal to F+4f+df, F5 is equal to F+5f+df, and F6 is equal toF+6f+df. Thus, all six of the actuator cylinders have a differentfrequency.

[0038] At this point, the testing system is permitted to operate, inthat the actuators are actuated. As shown in box 30, and by way of anon-limiting example, the system response (e.g., of the cylinders) ismeasured, calculated, or otherwise determined, specifically the energylevel (E), expressed in rms, peak G, or any other appropriate unit, andthe slope m, expressed as the slope of the fast Fourier transform of thesystem response (i.e., time history which is the slope of the energy vs.the frequency plot).

[0039] This information is then stored in a data storage medium and/ordevice (e.g., RAM, hard drive, floppy disk, CD-ROM, or the like) as anappropriate variable, under four different conditions, i.e., highpressure/high frequency (HH), high pressure/low frequency (HL), lowpressure/high frequency (LH), and low pressure/low frequency (LL).

[0040] As shown in box 40, and by way of a non-limiting example, thesystem response information generated is stored as eight differentvariables, i.e., E_(LL) (measured E when both P and F are low), E_(LH)(measured E when P is low and F is high), E_(HL) (measured E when P ishigh and F is low), E_(HH) (measured E when both P and F are high),m_(LL) (measured m when both P and F are low, m_(LH) (measured m when Pis low and F is high), m_(HL) (measured M when P is high and F is low),and m_(HH) (measured m when both P and F are high).

[0041] At this point, decision node 50 is encountered which querieswhether all four conditions have been tried (i.e., high/high, high/low,low/high, and low/low).

[0042] If all four conditions have not been tried, the control systemprompts a change in either the pressure, frequency, and/or both, of theindividual actuators, so that all four conditions are tried. As shown inBox 60, and by way of a non-limiting example, assuming that the firstcondition was low frequency/low pressure, then the first time changerequires a high frequency/low pressure condition, the second time changerequires a high frequency/high pressure condition, and the third timechange requires a low frequency/high pressure condition. It should benoted that the sequence of these conditions may in any desired order.The critical consideration is that all four conditions have been tried,not the order in which they are tried. The method of changing thepressure and/or frequency is by adding or removing appropriate levels ofpressure (i.e., ±dp) and/or frequency (i.e., ±df).

[0043] To illustrate this concept, consider the following non-limitingexample. Assume that the default P is 30 psi, and the dp is 10 psi.Therefore, the initial pressure is set at 40 psi (i.e., P (30 psi)+dp(10 psi)=40 psi), which represents the “high” pressure condition (i.e.,“plus” dp). Now, assume that the default frequency is 2 Hz, the stepfrequency is 0.2 Hz, and the df is 0.5 Hz. Therefore, the frequency ofthe first cylinder (F1) is 2.7 Hz (i.e., F(2 Hz)+f(0.2 Hz)+df(0.5Hz)=2.7 Hz), the second cylinder (F2) is 2.9 Hz (i.e., F(2 Hz)+2f (0.4Hz)+df(0.5 Hz)=2.9 Hz), the third cylinder (F3) is 3.1 Hz (i.e., F(2Hz)+3f(0.6 Hz)+df(0.5 Hz)=3.1 Hz), the fourth cylinder (F4) is 3.3 Hz(i.e., F(2 Hz)+4f(0.8 Hz)+df(0.5 Hz)=3.3 Hz), the fifth cylinder (F5) is3.5 Hz (i.e., F(2 Hz)+5f(1.0 Hz)+df(0.5 Hz)=3.5 Hz), and the sixthcylinder (F6) is 3.7 Hz (i.e., F (2 Hz)+6f(1.2 Hz)+df(0.5 Hz)=3.7 Hz),all of which represent the “high” frequency condition (i.e., “plus” df)

[0044] The apparatus is now operated under this particular highpressure/high frequency condition, the system response is measured (Box30), and the energy/slope variables are calculated and stored (Box 40),and then decision node 50 is encountered. As only one condition has beentried (i.e., high pressure/high frequency), the control system willprompt the apparatus to try the three remaining conditions (i.e., highpressure/low frequency, low pressure/low frequency, and lowpressure/high frequency).

[0045] With respect to the high pressure/low frequency condition,instead of adding the df Hz amount to each of the individual frequenciesof the actuators, it is removed or subtracted. Therefore, the frequencyof the first cylinder (F1) is 1.7 Hz (i.e., F(2 Hz)+f(0.2 Hz)+df (−0.5Hz)=1.7 Hz), the second cylinder (F2) is 1.9 Hz (i.e., F(2 Hz)+2f(0.4Hz)+df(−0.5 Hz)=1.9 Hz), the third cylinder (F3) is 3.1 Hz (i.e., F(2Hz)+3f(0.6 Hz) +df(−0.5 Hz)=2.1 Hz), the fourth cylinder (F4) is 2.3 Hz(i.e., F(2 Hz)+4f(0.8 Hz)+df(−0.5 Hz)=2.3 Hz), the fifth cylinder (F5)is 2.5 Hz (i.e., F(2 Hz)+5f(1.0 Hz)+df(−0.5 Hz)=2.5 Hz), and the sixthcylinder (F6) is 2.7 Hz (i.e., F(2 Hz)+6f(1.2 Hz)+df(−0.5 Hz)=2.7 Hz),all of which represent the “low” frequency condition (i.e., “minus” df).

[0046] The apparatus is now operated under this particular highpressure/low frequency condition, the system response is measured (Box30), and the energy/slope variables are calculated and stored (Box 40),and then decision node 50 is again encountered. As only two conditionshave been tried (i.e., high pressure/high frequency, high pressure/lowfrequency), the control system will prompt the apparatus to try the tworemaining conditions (i.e., low pressure/low frequency and lowpressure/high frequency).

[0047] With respect to the low pressure/low frequency condition, thefrequencies remain in the “low” condition; however, instead of addingthe dp psi amount to the pressure of the actuators, it is removed orsubtracted. Therefore, the pressure of all the cylinders is 20 psi(i.e., P(30 psi)−dp(10 psi)=20 psi), which represents the “low” pressurecondition (i.e., “minus” dp).

[0048] The apparatus is now operated under this particular lowpressure/low frequency condition, the system response is measured (Box30), and the energy/slope variables are calculated and stored (Box 40),and then decision node 50 is again encountered. As only three conditionshave been tried (i.e., high pressure/high frequency, high pressure/lowfrequency, low pressure/low frequency), the control system will promptthe apparatus to try the last remaining condition (i.e., and lowpressure/high frequency).

[0049] With respect to the low pressure/high frequency condition, thepressure remains in the “low” condition; however, instead of subtractingthe df Hz amount to the frequencies of each of the actuators, it isadded. Therefore, the frequency of the first cylinder (F1) is 2.7 Hz(i.e., F(2 Hz)+f(0.2 Hz)+df(0.5 Hz)=2.7 Hz), the second cylinder (F2) is2.9 Hz (i.e., F(2 Hz)+2f (0.4 Hz)+df(0.5 Hz)=2.9 Hz), the third cylinder(F3) is 3.1 Hz (i.e., F(2 Hz)+3f(0.6 Hz)+df(0.5 Hz)=3.1 Hz), the fourthcylinder (F4) is 3.3 Hz (i.e., F(2 Hz)+4f(0.8 Hz)+df(0.5 Hz)=3.3 Hz),the fifth cylinder (F5) is 3.5 Hz (i.e., F(2 Hz)+5f(1.0 Hz)+df(0.5 Hz)=3.5 Hz), and the sixth cylinder (F6) is 3.7 Hz (i.e., F (2 Hz)+6f(1.2Hz)+df(0.5 Hz)=3.7 Hz), all of which represent the “high” frequencycondition (i.e., “plus” df)

[0050] The apparatus is now operated under this particular lowpressure/high frequency condition, the system response is measured (Box30), and the energy/slope variables are calculated and stored (Box 40),and then decision node 50 is again encountered. As all four conditionshave now been tried (i.e., high pressure/high frequency, highpressure/low frequency, low pressure/low frequency, and lowpressure/high frequency), the system will then perform the calculationsof the algorithms shown in Box 70.

[0051] The first algorithm, shown below:

Dep=((E _(HH) +E _(HL))−(E _(LH) +E _(LL)))/(2dp)

[0052] is used to determine the change in energy due to pressure (Dep).

[0053] The second algorithm, shown below:

Def=((E _(HH) +E _(LH))−(E _(HL) +E _(LL)))/(2df)

[0054] is used to determine the change in energy due to frequency (Def).

[0055] The third algorithm, shown below:

Dsp=((m_(HH) +m _(HL))−(m _(LH) +m _(LL)))/(2dp)

[0056] is used to determine the change in slope due to pressure (Dsp).

[0057] The fourth algorithm, shown below:

Dsf=((m _(HH) +m _(LH))−(m _(HL) +m _(LL)))/(2df)

[0058] is used to determine the change in slope due to frequency (Dsf).

[0059] The fifth algorithm, shown below:

E 1=average (E _(HH) , E _(HL) , E _(LH) , E _(LL))

[0060] is used to determine the average energy for the highpressure/high frequency, high pressure/low frequency, low pressure/highfrequency, and low pressure/low frequency conditions.

[0061] The sixth algorithm, shown below:

S 1=average (m _(HH) , m _(HL) , m _(LH) , m _(LL))

[0062] is used to determine the average slope for the high pressure/highfrequency, high pressure/low frequency, low pressure/high frequency, andlow pressure/low frequency conditions.

[0063] The seventh algorithm, shown below:

E 2 =E 1+(E _(DESIRED) −E 1)/n

[0064] wherein n is greater than 1, is used to determine the new targetenergy (E2). It should be noted that the desired energy (E_(DESIRED)) ispre-selected by the operator.

[0065] The eighth algorithm, shown below:

S 2 =S 1+(S _(DESIRED) −S 1)/n

[0066] wherein n is greater than 1, is used to determine the new targetslope (S2). It should be noted that the desired slope (S_(DESIRED)) ispre-selected by the operator.

[0067] The ninth algorithm, shown below:

F _(NEW)=[(DspE 2 −DspE 1 −DepS 2 +DepS 1 −DepDsfF)/(DefDsp−DepDsf)]

[0068] is used to determine the new target frequency (F_(NEW)) toachieve the new target energy (E2). Once the F_(NEW) is determined, itreplaces F as the default frequency.

[0069] The tenth algorithm, shown below:

P _(NEW)=[(DsfE 2 −DsfE 1 −DefS 2 +DefS 1+DepDsfP−DefDspP)/(DefDsp−DepDsf)]

[0070] is used to determine the new target pressure (P_(NEW)) to achievethe new target slope (S2). Once the P_(NEW) is determined, it replaces Pas the default pressure.

[0071] Once all of the calculations have been performed for theabove-described algorithms, the system is then prompted to determinewhether the E_(DESIRED) and the S_(DESIRED) conditions have beensatisfied, as shown in Box 80. The determination with respect to theE_(DESIRED) and the S_(DESIRED) conditions are calculated according tothe following formulas:

E _(LL) <E _(DESIRED) <E _(HH)

and

m _(LL) <S _(DESIRED) <m _(HH)

[0072] wherein if both the E_(DESIRED) and the S_(DESIRED) conditionsfall between their respective formulaic extremes, the system is promptedto narrow the search, as shown in Box 90. The search is narrowed bydividing the dp and the df by n, respectively, wherein n is a numbergreater than 1. This has the intended effect of decreasing the amount ofchange in pressure and frequency, thus reducing the E_(LL)/E_(HH) andm_(LL)/m_(HH) ranges, respectively. The entire cycle is then repeated(starting at Box 20) with the new pressure and frequency defaults (i.e.,P_(NEW) and F_(NEW)), and is continued until the E_(DESIRED) and theS_(DESIRED) fall within the narrowed E_(LL)/E_(HH) and m_(LL)/m_(HH)ranges, respectively. By way of a non-limiting example, the cycle couldbe repeated until the narrowed E_(LL)/E_(HH) and m_(LL)/m_(HH) rangesare within a pre-selected percentage of the E_(DESIRED) and theS_(DESIRED), respectively. This process is continuously repeated duringthe operation of the apparatus to ensure that both the E_(DESIRED) andthe S_(DESIRED) fall within the narrowed E_(LL)/E_(HH) and m_(LL)/m_(HH)ranges.

[0073] However, if either one of the E_(DESIRED) and the S_(DESIRED)conditions do not fall between their respective formulaic extremes, thesystem is prompted to expand the search, as shown in Box 100. The searchis expanded by either multiplying the dp and the df by n (wherein n is anumber greater than 1), respectively, depending on whether theE_(DESIRED) or the S_(DESIRED) fell outside of the respective range.This has the intended effect of increasing the amount of change inpressure and/or frequency thus increasing the E_(LL)/E_(HH) and/orm_(LL)/m_(HH) ranges, respectively. The entire cycle is then repeated(starting at Box 20) with the new pressure and frequency defaults (i.e.,P_(NEW) and F_(NEW)), and is continued until the E_(DESIRED) and/or theS_(DESIRED) fall within the narrowed E_(LL)/E_(HH) and/or m_(LL)/m_(HH)ranges, respectively. By way of a non-limiting example, the cycle couldbe repeated until the expanded E_(LL)/E_(HH) and m_(LL)/m_(HH) rangesare within a pre-selected percentage of the E_(DESIRED) and theS_(DESIRED), respectively. This process is continuously repeated duringthe operation of the apparatus to ensure that both the E_(DESIRED) andthe S_(DESIRED) fall within the narrowed E_(LL)/E_(HH) and m_(LL)/m_(HH)ranges.

[0074] In accordance with another embodiment of the present invention, apressure dither system is provided for use in conjunction with a failuremode testing system. The pressure dither system will overcome thepreviously described problem of actuators having a tendency, due tofrictional forces and historesis, to gravitate towards a set point andget stuck, thus causing the actuators to improperly function.

[0075] Pressure dither involves the application and/or subtraction of asmall amount of pressure to or from the cylinder, generally on the orderof about 1-2 psi, either above or below the default pressure P and thechange in pressure dp.

[0076] The reason for employing a pressure dither is enhancedcontrollability. If the cylinder of the actuator is constantly at afixed pressure, even when running at the “high” pressure condition, itwill gravitate to a set point and get stuck, as previously described. Bydithering the pressure a slight amount, i.e., fluctuating the pressureslightly, this unwanted situation can be avoided. Specifically, theextension and/or retraction pressure of the actuator cylinder ispreferably slightly different (i.e., higher and/or lower as compared tothe fixed pressure) during each cycle, therefore, the probability thatthe cylinder will get stuck is decreased. It should be noted that thepressure dither system can be used either independent of, or inconjunction with the control system of the present invention.

[0077] With reference to FIG. 2, there is illustrated a schematic viewof pressure dither system for a failure mode testing system, inaccordance with one embodiment of the present invention. The pressuredither system can be incorporated into a software program that can beemployed to control and operate the failure mode testing system.

[0078] By way of a non-limiting example, an algorithm for determiningpressure dither (ditherp) is shown below:

ditherp=[((rnd)(maxdither))−((rnd)(maxdither2))]

[0079] wherein rnd is a random number function between 0 and 1, andmaxdither is the pre-selected maximum pressure difference for pressuredither (ditherp).

[0080] By way of a non-limiting example, the ditherp could be expressedas follows, assuming a rnd=1 and a maxdither of 1 psi were employed:

ditherp=[(1)(1 psi)]−[(1)(1 psi)(2)]=−0.5 psi

[0081] Thus, the ditherp would be −0.5 psi in this case, meaning thatthe pressure to the cylinder would be dithered by −0.5 psi. Once theditherp has been determined, the pressure during the extend phase(Extend) and retract phase (Retract) can then be calculated according tothe following algorithms:

Extend=P+ditherp

[0082] wherein P is the default pressure, and ditherp is the pressuredither, and

Retract=P+difference+ditherp

[0083] wherein P is the default pressure, difference is a pre-selectedpressure difference between the extend and retract pressures, andditherp is the pressure dither.

[0084] By way of a non-limiting example, the Extend pressure could beexpressed as follows, assuming a P=30 psi and a ditherp of −0.5 psi wereemployed:

Extend=30 psi+(−0.5 psi)=29.5 psi

[0085] By way of a non-limiting example, the Retract pressure could beexpressed as follows, assuming a P=30 psi, a difference (i.e., pressuredifference between the extend and retract pressures) of 5 psi, and aditherp of −0.5 psi were employed:

Retract=30 psi+5 psi+(−0.5 psi)=34.5 psi

[0086] Although the afore-mentioned pressure dither system algorithmsare especially suited for creating and maintaining the pressure dithersystem of the present invention, it should be noted that any othersuitable system or method for altering or changing the default pressuresupplied to the cylinder can be employed as well.

[0087] In accordance with yet another embodiment of the presentinvention, a frequency ringing system is provided for use in conjunctionwith a failure mode testing system. The frequency ringing system willovercome the previously described problem of actuators receiving lessenergy than the other actuators, causing the apparatus to drift towardthe actuator having the lowest energy level, resulting in performanceproblems.

[0088] The frequency ringing system involves reordering the frequencyassigned to a particular cylinder. The reordering can either be randomor cycled. The frequency ringing system does not involve changing theamount of any particular frequency itself(that is controlled by thecontrol system, specifically the control algorithm), but only thelocation of where that frequency is vis-a-vis the cylinders.

[0089] To illustrate this concept, consider the following non-limitingexample. Assume that the six actuator cylinders are assigned thefollowing respective frequencies: Cylinder 1—2 Hz; Cylinder 2—2.5 Hz,Cylinder 3—3 Hz; Cylinder 4—3.5 Hz, Cylinder 5—4 Hz; and Cylinder 6—4.5Hz. Now, if these frequencies did not change during the course of thetesting procedure, the apparatus would have a tendency to drift towardsCylinder 1, as it has the lowest frequency, and as explained previously,the lowest energy. Therefore, the present invention overcomes thisproblem by indexing, reordering or reassigning the various frequencies,regardless of their magnitude, to each of the cylinders so that no onecylinder remains at the same frequency for any extended period of time.It should be noted that present invention does not employ a simplerotation of the frequencies, i.e., moving the frequencies in orderaround the adjacent actuators, as that permits the formation of a“moving” or “roving” low energy actuator location. Therefore, instead ofthe low energy actuator being found at one particular actuator location,the low energy actuator is moving around all six actuator locations insequence. The reordering of the frequencies, in accordance with presentinvention, avoids this problem.

[0090] The time interval between the random assignments can be for anylength and can be either fixed or random. To illustrate this concept,assume that the cylinders originally are set at the followingfrequencies: Cylinder 1—2 Hz; Cylinder 2—2.5 Hz, Cylinder 3—3 Hz;Cylinder 4—3.5 Hz, Cylinder 5—4 Hz; and Cylinder 6—4.5 Hz, and that thefrequency ringing system has been programmed to randomly reorder thefrequencies every one second, for a total of six seconds. As anon-limiting example, the frequency information for each cylinder couldlook like that presented in Table 1 below: TABLE 1 Init. Time 1 Time 2Time 3 Time 4 Time 5 Time 6 Freq. Freq. Freq. Freq. Freq. Freq. Freq.Cyl.# (Hz) (Hz) (Hz) (Hz) (Hz) (Hz) (Hz) 1 2 2.5 4.5 3 4 3.5 2 2 2.5 4.52 4 3 2.5 3.5 3 3 2 3.5 2.5 4.5 3 4 4 3.5 3 2.5 3.5 2 4 4.5 5 4 3.5 4 22.5 4.5 3 6 4.5 4 3 4.5 3.5 2 2.5

[0091] As can be seen from Table 1, the cylinder location of thefrequencies listed above differ after each second has elapsed,therefore, no one cylinder retains the same frequency for any extendedperiod of time. It should be noted that the frequency ringing system canbe used either independent of, or in conjunction with either the controlsystem and/or the pressure dither system of the present invention.

[0092] With reference to FIG. 3, there is illustrated a schematic viewof frequency ringing system for a failure mode testing system, inaccordance with one embodiment of the present invention. The frequencyringing system can be incorporated into a software program that can beemployed to control and operate the failure mode testing system.

[0093] By way of a non-limiting example, an algorithm for determiningfrequency ringing is shown below:

Cylinder i=Mode(i+Mode(C 1, 6),6)+1

[0094] wherein i is the cylinder number (i.e., a number between 1 and6), Mode is the remainder of the quotient between any two given numbers,and C1 is the count number (e.g., any number representing a statuschange in the cylinder frequency location). Thus, count 1 is denotedherein as C1, count 2 is denoted as C2, and so forth. Each cylinder isassigned an initial frequency (e.g., cylinder 1 is assigned frequency 1(F1), cylinder 2 is assigned frequency 2 (F2), and so forth); thus, asthe frequency is indexed or reordered at each count, the frequencyassigned to a particular cylinder is changed (which can be abbreviatedas cyli).

[0095] By way of a non-limiting example, the frequency ringing system asapplied to cylinders 1-6 through an eight count series (e.g., 1-8) isillustrated below:

[0096] Count 1

[0097] Cylinder 1=Mode(1+Mode(1, 6),6)+1

[0098] Cylinder 1=Mode(1+1,6)+1

[0099] Cylinder 1=Mode(2,6)+1

[0100] Cylinder 1=2+1

[0101] Cylinder 1=3

[0102] Thus, cylinder 1 at count 1 is assigned frequency 3.

[0103] Count 2

[0104] Cylinder 1=Mode(1+Mode(2, 6),6)+1

[0105] Cylinder 1=Mode(1+2,6)+1

[0106] Cylinder 1=Mode(3,6)+1

[0107] Cylinder 1=3+1

[0108] Cylinder 1=4

[0109] Thus, cylinder 1 at count 2 is assigned frequency 4.

[0110] Count 3

[0111] Cylinder 1=Mode(1+Mode(3, 6),6)+1

[0112] Cylinder 1=Mode(1+3,6)+1

[0113] Cylinder 1=Mode(4,6)+1

[0114] Cylinder 1=4+1

[0115] Cylinder 1=5

[0116] Thus, cylinder 1 at count 3 is assigned frequency 5.

[0117] Count 4

[0118] Cylinder 1=Mode(1+Mode(4, 6),6)+1

[0119] Cylinder 1=Mode(1+4,6)+1

[0120] Cylinder 1=Mode(5,6)+1

[0121] Cylinder 1=5+1

[0122] Cylinder 1=6

[0123] Thus, cylinder 1 at count 4 is assigned frequency 6.

[0124] Count 5

[0125] Cylinder 1=Mode(1+Mode(5, 6),6)+1

[0126] Cylinder 1=Mode(1+5,6)+1

[0127] Cylinder 1=Mode(6,6)+1

[0128] Cylinder 1=0+1

[0129] Cylinder 1=1

[0130] Thus, cylinder 1 at count 5 is assigned frequency 1.

[0131] Count 6

[0132] Cylinder 1=Mode(1+Mode(6, 6),6)+1

[0133] Cylinder 1=Mode(1+0,6)+1

[0134] Cylinder 1=Mode(1,6)+1

[0135] Cylinder 1=1+1

[0136] Cylinder 1=2

[0137] Thus, cylinder 1 at count 6 is assigned frequency 2.

[0138] Count 7

[0139] Cylinder 1=Mode(1+Mode(7, 6),6)+1

[0140] Cylinder 1=Mode(1+7,6)+1

[0141] Cylinder 1=Mode(8,6)+1

[0142] Cylinder 1=2+1

[0143] Cylinder 1=3

[0144] Thus, cylinder 1 at count 7 is assigned frequency 3.

[0145] Count 8

[0146] Cylinder 1=Mode(1+Mode(8, 6),6)+1

[0147] Cylinder 1=Mode(1+8,6)+1

[0148] Cylinder 1=Mode(9,6)+1

[0149] Cylinder 1=3+1

[0150] Cylinder 1=4

[0151] Thus, cylinder 1 at count 8 is assigned frequency 4.

[0152] By way of a non-limiting example, the frequency ringing system asapplied to cylinder 2 through an eight count series (e.g., 1-8) isillustrated below:

[0153] Count 1

[0154] Cylinder 2=Mode(2+Mode(1, 6),6)+1

[0155] Cylinder 2=Mode(2+1,6)+1

[0156] Cylinder 2=Mode(3,6)+1

[0157] Cylinder 2=3+1

[0158] Cylinder 2=4

[0159] Thus, cylinder 2 at count 1 is assigned frequency 4.

[0160] Count 2

[0161] Cylinder 2=Mode(2+Mode(2, 6),6)+1

[0162] Cylinder 2=Mode(2+2,6)+1

[0163] Cylinder 2=Mode(4,6)+1

[0164] Cylinder 2=4+1

[0165] Cylinder 2=5

[0166] Thus, cylinder 2 at count 2 is assigned frequency 5.

[0167] Count 3

[0168] Cylinder 2=Mode(2+Mode(3, 6),6)+1

[0169] Cylinder 2=Mode(2+3,6)+1

[0170] Cylinder 2=Mode(5,6)+1

[0171] Cylinder 2=5+1

[0172] Cylinder 2=6

[0173] Thus, cylinder 2 at count 3 is assigned frequency 6.

[0174] Count 4

[0175] Cylinder 2=Mode(2+Mode(4, 6),6)+1

[0176] Cylinder 2=Mode(2+4,6)+1

[0177] Cylinder 2=Mode(6,6)+1

[0178] Cylinder 2=0+1

[0179] Cylinder 2=1

[0180] Thus, cylinder 2 at count 4 is assigned frequency 1.

[0181] Count 5

[0182] Cylinder 2=Mode(2+Mode(5, 6),6)+1

[0183] Cylinder 2=Mode(2+5,6)+1

[0184] Cylinder 2=Mode(7,6)+1

[0185] Cylinder 2=1+1

[0186] Cylinder 2=2

[0187] Thus, cylinder 2 at count 5 is assigned frequency 2.

[0188] Count 6

[0189] Cylinder 2=Mode(2+Mode(6, 6),6)+1

[0190] Cylinder 2=Mode(2+0,6)+1

[0191] Cylinder 2=Mode(2,6)+1

[0192] Cylinder 2=2+1

[0193] Cylinder 2=3

[0194] Thus, cylinder 2 at count 6 is assigned frequency 3.

[0195] Count 7

[0196] Cylinder 2=Mode(2+Mode(7, 6),6)+1

[0197] Cylinder 2=Mode(2+7,6)+1

[0198] Cylinder 2=Mode(9,6)+1

[0199] Cylinder 2=3+1

[0200] Cylinder 2=4

[0201] Thus, cylinder 2 at count 7 is assigned frequency 4.

[0202] Count 8

[0203] Cylinder 2=Mode(2+Mode(8, 6),6)+1

[0204] Cylinder 2=Mode(2+8,6)+1

[0205] Cylinder 2=Mode(10,6)+1

[0206] Cylinder 2=4+1

[0207] Cylinder 2=5

[0208] Thus, cylinder 2 at count 8 is assigned frequency 5.

[0209] By way of a non-limiting example, the frequency ringing system asapplied to cylinder 3 through an eight count series (e.g., 1-8) isillustrated below:

[0210] Count 1

[0211] Cylinder 3=Mode(3+Mode(1, 6),6)+1

[0212] Cylinder 3=Mode(3+1,6)+1

[0213] Cylinder 3=Mode(4,6)+1

[0214] Cylinder 3=4+1

[0215] Cylinder 3=5

[0216] Thus, cylinder 3 at count 1 is assigned frequency 5.

[0217] Count 2

[0218] Cylinder 3=Mode(3+Mode(2, 6),6)+1

[0219] Cylinder 3=Mode(3+2,6)+1

[0220] Cylinder 3=Mode(5,6)+1

[0221] Cylinder 3=5+1

[0222] Cylinder 3=6

[0223] Thus, cylinder 3 at count 2 is assigned frequency 6.

[0224] Count 3

[0225] Cylinder 3=Mode(3+Mode(3, 6),6)+1

[0226] Cylinder 3=Mode(3+3,6)+1

[0227] Cylinder 3=Mode(6,6)+1

[0228] Cylinder 3=0+1

[0229] Cylinder 3=1

[0230] Thus, cylinder 3 at count 3 is assigned frequency 1.

[0231] Count 4

[0232] Cylinder 3=Mode(3+Mode(4, 6),6)+1

[0233] Cylinder 3=Mode(3+4,6)+1

[0234] Cylinder 3=Mode(7,6)+1

[0235] Cylinder 3=1+1

[0236] Cylinder 3=2

[0237] Thus, cylinder 3 at count 4 is assigned frequency 2.

[0238] Count 5

[0239] Cylinder 3=Mode(3+Mode(5, 6),6)+1

[0240] Cylinder 3=Mode(3+5,6)+1

[0241] Cylinder 3=Mode(8,6)+1

[0242] Cylinder 3=2+1

[0243] Cylinder 3=3

[0244] Thus, cylinder 2 at count 5 is assigned frequency 3.

[0245] Count 6

[0246] Cylinder 3=Mode(3+Mode(6, 6),6)+1

[0247] Cylinder 3=Mode(3+0,6)+1

[0248] Cylinder 3=Mode(3,6)+1

[0249] Cylinder 3=3+1

[0250] Cylinder 3=4

[0251] Thus, cylinder 2 at count 6 is assigned frequency 4.

[0252] Count 7

[0253] Cylinder 3=Mode(3+Mode(7, 6),6)+1

[0254] Cylinder 3=Mode(3+7,6)+1

[0255] Cylinder 3=Mode(10,6)+1

[0256] Cylinder 3=4+1

[0257] Cylinder 3=5

[0258] Thus, cylinder 3 at count 7 is assigned frequency 5.

[0259] Count 8

[0260] Cylinder 3=Mode(3+Mode(8, 6),6)+1

[0261] Cylinder 3=Mode(3+8,6)+1

[0262] Cylinder 3=Mode(11,6)+1

[0263] Cylinder 3=5+1

[0264] Cylinder 3=6

[0265] Thus, cylinder 3 at count 8 is assigned frequency 6.

[0266] By way of a non-limiting example, the frequency ringing system asapplied to cylinder 4 through an eight count series (e.g., 1-8) isillustrated below:

[0267] Count 1

[0268] Cylinder 4=Mode(4+Mode(1, 6),6)+1

[0269] Cylinder 4=Mode(4+1,6)+1

[0270] Cylinder 4=Mode(5,6)+1

[0271] Cylinder 4=5+1

[0272] Cylinder 4=6

[0273] Thus, cylinder 4 at count 1 is assigned frequency 6.

[0274] Count 2

[0275] Cylinder 4=Mode(4+Mode(2, 6),6)+1

[0276] Cylinder 4=Mode(4+2,6)+1

[0277] Cylinder 4=Mode(6,6)+1

[0278] Cylinder 4=0+1

[0279] Cylinder 4=1

[0280] Thus, cylinder 4 at count 2 is assigned frequency 1.

[0281] Count 3

[0282] Cylinder 4=Mode(4+Mode(3, 6),6)+1

[0283] Cylinder 4=Mode(4+3,6)+1

[0284] Cylinder 4=Mode(7,6)+1

[0285] Cylinder 4=1+1

[0286] Cylinder 4=2

[0287] Thus, cylinder 4 at count 3 is assigned frequency 2.

[0288] Count 4

[0289] Cylinder 4=Mode(4+Mode(4, 6),6)+1

[0290] Cylinder 4=Mode(4+4,6)+1

[0291] Cylinder 4=Mode(8,6)+1

[0292] Cylinder 4=2+1

[0293] Cylinder 4=3

[0294] Thus, cylinder 4 at count 4 his assigned frequency 3.

[0295] Count 5

[0296] Cylinder 4=Mode(4+Mode(5, 6),6)+1

[0297] Cylinder 4=Mode(4+5,6)+1

[0298] Cylinder 4=Mode(9,6)+1

[0299] Cylinder 4=3+1

[0300] Cylinder 4=4

[0301] Thus, cylinder 4 at count 5 is assigned frequency 4.

[0302] Count 6

[0303] Cylinder 4=Mode(4+Mode(6, 6),6)+1

[0304] Cylinder 4=Mode(4+0,6)+1

[0305] Cylinder 4=Mode(4,6)+1

[0306] Cylinder 4=4+1

[0307] Cylinder 4=5

[0308] Thus, cylinder 4 at count 6 is assigned frequency 5.

[0309] Count 7

[0310] Cylinder 4=Mode(4+Mode(7, 6),6)+1

[0311] Cylinder 4=Mode(4+1,6)+1

[0312] Cylinder 4=Mode(5,6)+1

[0313] Cylinder 4=5+1

[0314] Cylinder 4=6

[0315] Thus, cylinder 4 at count 7 is assigned frequency 6.

[0316] Count 8

[0317] Cylinder 4=Mode(4+Mode(8, 6),6)+1

[0318] Cylinder 4=Mode(4+2,6)+1

[0319] Cylinder 4=Mode(6,6)+1

[0320] Cylinder 4=0+1

[0321] Cylinder 4=1

[0322] Thus, cylinder 4 at count 8 is assigned frequency 1.

[0323] By way of a non-limiting example, the frequency ringing system asapplied to cylinder 5 through a six count series (e.g., 1-6) isillustrated below:

[0324] Count 1

[0325] Cylinder 5=Mode(5+Mode(1, 6),6)+1

[0326] Cylinder 5=Mode(5+1,6)+1

[0327] Cylinder 5=Mode(6,6)+1

[0328] Cylinder 5=0+1

[0329] Cylinder 5=1

[0330] Thus, cylinder 5 at count 1 is assigned frequency 1.

[0331] Count 2

[0332] Cylinder 5=Mode(5+Mode(2, 6),6)+1

[0333] Cylinder 5=Mode(5+2,6)+1

[0334] Cylinder 5=Mode(7,6)+1

[0335] Cylinder 5=1+1

[0336] Cylinder 5=2

[0337] Thus, cylinder 5 at count 2 is assigned frequency 2.

[0338] Count 3

[0339] Cylinder 5=Mode(5+Mode(3, 6),6)+1

[0340] Cylinder 5=Mode(5+3,6)+1

[0341] Cylinder 5=Mode(8,6)+1

[0342] Cylinder 5=2+1

[0343] Cylinder 5=3

[0344] Thus, cylinder 5 at count 3 is assigned frequency 3.

[0345] Count 4

[0346] Cylinder 5=Mode(5+Mode(4, 6),6)+1

[0347] Cylinder 5=Mode(5+4,6)+1

[0348] Cylinder 5=Mode(9,6)+1

[0349] Cylinder 5=3+1

[0350] Cylinder 5=4

[0351] Thus, cylinder 5 at count 4 is assigned frequency 4.

[0352] Count 5

[0353] Cylinder 5=Mode(5+Mode(5, 6),6)+1

[0354] Cylinder 5=Mode(5+5,6)+1

[0355] Cylinder 5=Mode(10,6)+1

[0356] Cylinder 5=4+1

[0357] Cylinder 5=5

[0358] Thus, cylinder 5 at count 5 is assigned frequency 5.

[0359] Count 6

[0360] Cylinder 5=Mode(5+Mode(6, 6),6)+1

[0361] Cylinder 5=Mode(5+0,6)+1

[0362] Cylinder 5=Mode(5,6)+1

[0363] Cylinder 5=5+1

[0364] Cylinder 5=6

[0365] Thus, cylinder 5 at count 6 is assigned frequency 6.

[0366] Count 7

[0367] Cylinder 5=Mode(5+Mode(7, 6),6)+1

[0368] Cylinder 5=Mode(5+1,6)+1

[0369] Cylinder 5=Mode(6,6)+1

[0370] Cylinder 5=0+1

[0371] Cylinder 5=1

[0372] Thus, cylinder 5 at count 7 is assigned frequency 1.

[0373] Count 8

[0374] Cylinder 5=Mode(5+Mode(8, 6),6)+1

[0375] Cylinder 5=Mode(5+2,6)+1

[0376] Cylinder 5=Mode(7,6)+1

[0377] Cylinder 5=1+1

[0378] Cylinder 5=2

[0379] Thus, cylinder 5 at count 8 is assigned frequency 2.

[0380] By way of a non-limiting example, the frequency ringing system asapplied to cylinder 6 through an eight count series (e.g., 1-8) isillustrated below:

[0381] Count 1

[0382] Cylinder 6=Mode(6+Mode(1, 6),6)+1

[0383] Cylinder 6=Mode(6+1,6)+1

[0384] Cylinder 6=Mode(7,6)+1

[0385] Cylinder 6=1+1

[0386] Cylinder 6=2

[0387] Thus, cylinder 6 at count 1 is assigned frequency 2.

[0388] Count 2

[0389] Cylinder 6=Mode(6+Mode(2, 6),6)+1

[0390] Cylinder 6=Mode(6+2,6)+1

[0391] Cylinder 6=Mode(8,6)+1

[0392] Cylinder 6=2+1

[0393] Cylinder 6=3

[0394] Thus, cylinder 6 at count 2 is assigned frequency 3.

[0395] Count 3

[0396] Cylinder 6=Mode(6+Mode(3, 6),6)+1

[0397] Cylinder 6=Mode(6+3,6)+1

[0398] Cylinder 6=Mode(9,6)+1

[0399] Cylinder 6=3+1

[0400] Cylinder 6=4

[0401] Thus, cylinder 6 at count 3 is assigned frequency 4.

[0402] Count 4

[0403] Cylinder 6=Mode(6+Mode(4, 6),6)+1

[0404] Cylinder 6=Mode(6+4,6)+1

[0405] Cylinder 6=Mode(10,6)+1

[0406] Cylinder 6=4+1

[0407] Cylinder 6=5

[0408] Thus, cylinder 6 at count 4 is assigned frequency 5.

[0409] Count 5

[0410] Cylinder 6=Mode(6+Mode(5, 6),6)+1

[0411] Cylinder 6=Mode(6+5,6)+1

[0412] Cylinder 6=Mode(11,6)+1

[0413] Cylinder 6=5+1

[0414] Cylinder 6=6

[0415] Thus, cylinder 6 at count 5 is assigned frequency 6.

[0416] Count 6

[0417] Cylinder 6=Mode(6+Mode(6, 6),6)+1

[0418] Cylinder 6=Mode(6+0,6)+1

[0419] Cylinder 6=Mode(6,6)+1

[0420] Cylinder 6=0+1

[0421] Cylinder 6=1

[0422] Thus, cylinder 6 at count 6 is assigned frequency 1.

[0423] Count 7

[0424] Cylinder 6=Mode(6+Mode(7, 6),6)+1

[0425] Cylinder 6=Mode(6+1,6)+1

[0426] Cylinder 6=Mode(7,6)+1

[0427] Cylinder 6=1+1

[0428] Cylinder 6=2

[0429] Thus, cylinder 6 at count 7 is assigned frequency 2.

[0430] Count 8

[0431] Cylinder 6=Mode(6+Mode(8, 6),6)+1

[0432] Cylinder 6=Mode(6+2,6)+1

[0433] Cylinder 6=Mode(8,6)+1

[0434] Cylinder 6=2+1

[0435] Cylinder 6=3

[0436] Thus, cylinder 6 at count 8 is assigned frequency 3.

[0437] The corresponding cylinder frequencies of the various cylindersat each of the eight counts is presented in Table 2, below: TABLE 2 C1C2 C3 C4 C5 C6 C7 C8 Cyl.# Cyl.# Cyl.# Cyl.# Cyl.# Cyl.# Cyl.# Cyl.#Cyl.# Freq. Freq. Freq. Freq. Freq. Freq. Freq. Freq. 1 2 3 4 5 6 1 2 32 3 4 5 6 1 2 3 4 3 4 5 6 1 2 3 4 5 4 5 6 1 2 3 4 5 6 5 6 1 2 3 4 5 6 16 1 2 3 4 5 6 1 2

[0438] As can be seen from Table 2, the frequency initially assigned toa particular cylinder location is being indexed or reordered among thesix cylinders in such a manner that after each count, an individualcylinder's frequency has changed. Additionally, it should be noted thatthe frequencies are not indexed in a sequential manner such that thefrequencies initially assigned to adjacent cylinders move lock steparound in a circle. As previously noted, that would merely cause thelow-energy site to move circularly around the actuator assemblies. Thepresent invention avoids this problem by ensuring that, sometime duringa count sequence, at least one individual cylinder has a frequency of anon-adjacent cylinder.

[0439] Thus, after each count, the frequency of a particular cylinder ischanged according to the following algorithm:

C 1 =C 1+1

[0440] wherein C1 is the count number (e.g., any number representing astatus change in the cylinder frequency location). Thus after count 1,the frequency of a particular cylinder would be changed to thatcorresponding to count 2, and so forth.

[0441] Although the afore-mentioned frequency ringing system algorithmsare especially suited for creating and maintaining the frequency ringingsystem of the present invention, it should be noted that any othersuitable system or method for indexing the frequencies assigned to thecylinders can be employed as well.

[0442] As previously mentioned, the control system, the pressure dithersystem, and the frequency ringing system, can be incorporated intocomputer software programs, either independently or combined in variouscombinations.

[0443] With reference to FIG. 4, there is illustrated a schematic viewof a computer software program for a control system for a failure modetesting system, in accordance with one embodiment of the invention.

[0444] With reference to FIG. 5, there is illustrated a schematic viewof a computer software program for a control system for a failure modetesting system employing both a pressure dither system and a frequencyringing system, in accordance with one embodiment of the invention.

[0445] The foregoing description is considered illustrative only of theprinciples of the invention. Furthermore, since numerous modificationsand changes will readily occur to those skilled in the art, it is notdesired to limit the invention to the exact construction and processshown as described above. Accordingly, all suitable modifications andequivalents may be resorted to falling within the scope of the inventionas defined by the claims which follow.

What is claimed is:
 1. A control system for a failure mode testingsystem having a determinable system response, wherein the testing systemincludes a plurality of actuator cylinders, each cylinder operating atan initial pressure and an initial frequency, wherein the frequency ofeach of the cylinders is different, comprising: a) selecting a desiredenergy level of the system response; b) selecting a desired slope of thefast Fourier transform of the system response; c) changing anoperational parameter of the cylinders by a pre-selected amount in orderto create a first pressure/frequency condition, wherein the operationalparameter is selected from the group consisting of pressure, frequency,and combinations thereof; d) determining the system response in terms ofenergy and slope of the fast Fourier transform of the system responseunder the first pressure/frequency condition; and e) storing the systemresponse determination of the first pressure/frequency condition in adata storage medium.
 2. The control system in accordance with claim 1,further comprising: f) changing an operational parameter of thecylinders by a pre-selected amount in order to create a secondpressure/frequency condition different from the first pressure/frequencycondition; g) determining the system response in terms of energy andslope of the fast Fourier transform of the system response under thesecond pressure/frequency condition; and h) storing the system responsedetermination of the second pressure/frequency condition in a datastorage medium.
 3. The control system in accordance with claim 2,further comprising: i) changing an operational parameter of thecylinders by a pre-selected amount in order to create a thirdpressure/frequency condition different from the first and secondpressure/frequency conditions; j) determining the system response interms of energy and slope of the fast Fourier transform of the systemresponse under the third pressure/frequency condition; and k) storingthe system response determination of the third pressure/frequencycondition in a data storage medium.
 4. The control system in accordancewith claim 3, further comprising: l) changing an operational parameterof the cylinders by a pre-selected amount in order to create a fourthpressure/frequency condition different from the first, second, and thirdpressure/frequency conditions; m) determining the system response interms of energy and slope of the fast Fourier transform of the systemresponse under the fourth pressure/frequency condition; and n) storingthe system response determination of the fourth pressure/frequencycondition in a data storage medium.
 5. The control system in accordancewith claim 4, further comprising: o) determining whether the desiredenergy level of the system response falls within the range defined bythe measured energy level of any of the pressure/frequency conditionsaccording to the formula: E_(LL)<E_(DESIRED)<E_(HH), wherein E_(LL) isthe energy measured during a pressure/frequency condition correspondingto a low pressure/low frequency condition, E_(DESIRED) is the desiredenergy level of the system response, and E_(HH) is the energy measuredduring a pressure/frequency condition corresponding to a highpressure/high frequency condition; and p) determining whether thedesired slope of the fast Fourier transform of the system response fallswithin the range defined by the measured slope of the fast Fouriertransform of the system response of any of the pressure/frequencyconditions according to the formula: m_(LL)<m_(DESIRED)<m_(HH), whereinm_(LL) is the slope of the fast Fourier transform of the system responsemeasured during a pressure/frequency condition corresponding to a lowpressure/low frequency condition, m_(DESIRED) is the desired slope ofthe fast Fourier transform of the system response of the cylinder, andm_(HH) is the slope of the fast Fourier transform of the system responsemeasured during a pressure/frequency condition corresponding to a highpressure/high frequency condition.
 6. The control system in accordancewith claim 5, further comprising: q) decreasing the pre-selected amountthat the operational parameter is changed by and repeating steps c)through p), if the desired energy level of the system response does fallwithin the range defined by the measured energy level of apressure/frequency condition corresponding to a low pressure/lowfrequency condition and a pressure/frequency condition corresponding toa high pressure/high frequency condition.
 7. The control system inaccordance with claim 5, further comprising: r) increasing thepre-selected amount that the operational parameter is increased by andrepeating steps c) through p), if the desired energy level of the systemresponse does not fall within the range defined by the measured energylevel of a pressure/frequency condition corresponding to a lowpressure/low frequency condition and a pressure/frequency conditioncorresponding to a high pressure/high frequency condition.
 8. Thecontrol system in accordance with claim 5, further comprising: s)decreasing the pre-selected amount that the operational parameter ischanged by and repeating steps c) through p), if the desired slope ofthe fast Fourier transform of the system response does fall within therange defined by the measured slope of the fast Fourier transform of thesystem response of a pressure/frequency condition corresponding to a lowpressure/low frequency condition and a pressure/frequency conditioncorresponding to a high pressure/high frequency condition.
 9. Thecontrol system in accordance with claim 5, further comprising: t)increasing the pre-selected amount that the operational parameter ischanged by and repeating steps c) through p), if the desired slope ofthe fast Fourier transform of the system response does not fall withinthe range defined by the measured slope of the fast Fourier transform ofthe system response of a pressure/frequency condition corresponding to alow pressure/low frequency condition and a pressure/frequency conditioncorresponding to a high pressure/high frequency condition.
 10. Thecontrol system in accordance with claim 5, further comprising: u)calculating the change in energy due to pressure (Dep) according to theformula: Dep=((E_(HH)+E_(HL))−(E_(LH)+E_(LL)))/(2dp), wherein E_(HH) isthe energy measured during a pressure/frequency condition correspondingto a high pressure/high frequency condition, E_(HL) is the energymeasured during a pressure/frequency condition corresponding to a highpressure/low frequency condition, E_(LH) is the energy measured during apressure/frequency condition corresponding to a low pressure/highfrequency condition, E_(LL) is the energy measured during apressure/frequency condition corresponding to a low pressure/lowfrequency condition, and dp is the pre-selected amount by which thepressure is either increased or decreased.
 11. The control system inaccordance with claim 5, further comprising: v) calculating the changein energy due to frequency (Def) according to the formula:Def=((E_(HH)+E_(LH))−(_(LHL)+E_(LL)))/(2df), wherein E_(HH) is theenergy measured during a pressure/frequency condition corresponding to ahigh pressure/high frequency condition, E_(LH) is the energy measuredduring a pressure/frequency condition corresponding to a lowpressure/high frequency condition, E_(HL) is the energy measured duringa pressure/frequency condition corresponding to a high pressure/lowfrequency condition, E_(LL) is the energy measured during apressure/frequency condition corresponding to a low pressure/lowfrequency condition, and df is the pre-selected amount by which thefrequency is either increased or decreased.
 12. The control system inaccordance with claim 5, further comprising: w) calculating the changein slope of the fast Fourier transform of the frequency due to pressure(Dsp) according to the formula:Dsp=((m_(HH)+m_(HL))−(m_(LH)+m_(LL)))/(2dp), wherein m_(HH) is the slopeof the fast Fourier transform of the system response measured during apressure/frequency condition corresponding to a high pressure/highfrequency condition, m_(HL) is the slope of the fast Fourier transformof the system response measured during a pressure/frequency conditioncorresponding to a high pressure/low frequency condition, m_(LH) is theslope of the fast Fourier transform of the system response measuredduring a pressure/frequency condition corresponding to a lowpressure/high frequency condition, m_(LL) is the slope of the fastFourier transform of the system response measured during apressure/frequency condition corresponding to a low pressure/lowfrequency condition, and dp is the pre-selected amount by which thepressure is either increased or decreased.
 13. The control system inaccordance with claim 5, further comprising: x) calculating the changein slope of the fast Fourier transform of the system response due tofrequency (Dsf) according to the formula:Dsf=((m_(HH)+m_(LH))−(m_(HL)+m_(LL)))/(2df), wherein m_(HH) is the slopeof the fast Fourier transform of the system response measured during apressure/frequency condition corresponding to a high pressure/highfrequency condition, m_(LH) is the slope of the fast Fourier transformof the system response measured during a pressure/frequency conditioncorresponding to a low pressure/high frequency condition, m_(HL) is theslope of the fast Fourier transform of the system response measuredduring a pressure/frequency condition corresponding to a highpressure/low frequency condition, m_(LL) is the slope of the fastFourier transform of the system response measured during apressure/frequency condition corresponding to a low pressure/lowfrequency condition, and df is the pre-selected amount by which thefrequency is either increased or decreased.
 14. The control system inaccordance with claim 5, further comprising: y) calculating the averageenergy (E1) according to the following formula: E1=average (E_(HH),E_(HL), E_(LH), E_(LL)), wherein E_(HH) is the energy measured during apressure/frequency condition corresponding to a high pressure/highfrequency condition, E_(HL) is the energy measured during apressure/frequency condition corresponding to a high pressure/lowfrequency condition, E_(LH) is the energy measured during apressure/frequency condition corresponding to a low pressure/highfrequency condition, and E_(LL) is the energy measured during apressure/frequency condition corresponding to a low pressure/lowfrequency condition.
 15. The control system in accordance with claim 14,further comprising: z) calculating the new target energy (E2) accordingto the following formula: E2=E1+(E_(DESIRE)−E1)/n, wherein E1 is theaverage energy, E_(DESIRED) is the desired energy level of the cylinder,and n is a number greater than
 1. 16. The control system in accordancewith claim 15, further comprising: aa) calculating the average slope ofthe fast Fourier transform of the system response (S1) according to thefollowing formula: S1=average (m_(HH), m_(HL), m_(LH), m_(LL)), whereinm_(HH) is the slope of the fast Fourier transform of the system responsemeasured during a pressure/frequency condition corresponding to a highpressure/high frequency condition, m_(HL) is the slope of the fastFourier transform of the system measured during a pressure/frequencycondition corresponding to a high pressure/low frequency condition,m_(LH) is the slope of the fast Fourier transform of the system responsemeasured during a pressure/frequency condition corresponding to a lowpressure/high frequency condition, and m_(LL) is the slope of the fastFourier transform of the system response measured during apressure/frequency condition corresponding to a low pressure/lowfrequency condition.
 17. The control system in accordance with claim 16,further comprising: bb) calculating the new target slope of the fastFourier transform of the system response (S2) according to the followingformula: S2=S1+(S_(DESIRED)−S1)/n, wherein S1 is the average slope ofthe fast Fourier transform of the system response, S_(DESIRED) is thedesired slope of the fast Fourier transform of the system response, andn is a number greater than
 1. 18. The control system in accordance withclaim 17, further comprising: cc) calculating the new target pressure(P_(NEW)) according to the formula:P_(NEW)=[(DsfE2−DsfE1−DefS2+DefS1−DepDsfP)/(DefDsp−DepDsf)], wherein Defis the change in energy due to frequency, Dep is the change in energydue to pressure, Dsf is the change in slope of the fast Fouriertransform of the system response due to frequency, Dsp is the change inslope of the fast Fourier transform of the system response due topressure, E1 is the average energy, E2 is the new target energy, S1 isthe average slope of the fast Fourier transform of the system response,and S2 is the new target slope of the fast Fourier transform of thesystem response.
 19. The control system in accordance with claim 18,further comprising: dd) substituting the new target pressure (P_(NEW))for the initial pressure and repeating steps c) through p).
 20. Thecontrol system in accordance with claim 17, further comprising: ee)calculating the new target frequency (F_(NEW)) according to the formula:F_(NEW)=[(DspE2−DspE1−DepS2+DepS1−DepDsfF)/(DefDsp−DepDsf)], wherein Defis the change in energy due to frequency, Dep is the change in energydue to pressure, Dsf is the change in slope of the fast Fouriertransform of the system response due to frequency, Dsp is the change inslope of the fast Fourier transform of the system response due topressure, E1 is the average energy, E2 is the new target energy, S1 isthe average slope of the fast Fourier transform of the system response,and S2 is the new target slope of the fast Fourier transform of thesystem response.
 21. The control system in accordance with claim 20,further comprising: ff) substituting the new target frequency (F_(NEW))for the initial frequency and repeating steps c) through p).
 22. Thecontrol system in accordance with claim 1, further comprising: apressure dither system, wherein the pressure of the actuator cylinderduring extension and retraction is changed by an incremental amount ofpressure (ditherp).
 23. The control system in accordance with claim 22,wherein the dither pressure (ditherp) is calculated in accordance withthe formula: [((rnd)(maxdither))−((rnd)(maxdither2))], wherein rnd is arandom number function between 0 and 1, and maxdither is thepre-selected maximum pressure difference for dither pressure (ditherp).24. The control system in accordance with claim 1, further comprising: afrequency ringing system, wherein the location of a particular frequencyis reordered among the plurality of actuator cylinders.
 25. The controlsystem in accordance with claim 24, wherein the frequency ringing systemis calculated in accordance with the formula: cylinder i=Mode(i+Mode(C1,6),6)+1, wherein i is the cylinder number, Mode is the remainder of thequotient between any two given numbers, and C1 is the count numberrepresenting a status change in the cylinder frequency location.
 26. Acontrol system for a failure mode testing system having a determinablesystem response, wherein the testing system includes a plurality ofactuator cylinders, each cylinder operating at a pressure and afrequency, wherein the frequency of each of the cylinders is different,comprising: a) selecting a desired energy level of the system response;b) selecting a desired slope of the fast Fourier transform of the systemresponse; c) determining the energy level under a high pressure/highfrequency condition and a low pressure/low frequency condition so as todefine an energy level range; d) determining the slope of the fastFourier transform of the system response under a high pressure/highfrequency condition and a low pressure/low frequency condition so as todefine a slope range; e) determining whether the desired energy levelfalls within the energy level range; and f) determining whether thedesired slope of the fast Fourier transform of the system response fallswithin the slope range.
 27. The control system in accordance with claim26, further comprising: g) decreasing the pressure and repeating stepsa) through f), if the desired energy level of the system response doesfall within the energy level range.
 28. The control system in accordancewith claim 26, further comprising: h) increasing the pressure andrepeating steps a) through f), if the desired energy level of the systemresponse does not fall within the energy level range.
 29. The controlsystem in accordance with claim 26, further comprising: i) decreasingthe frequency and repeating steps a) through f), if the desired slope ofthe fast Fourier transform of the system response does fall within theslope range.
 30. The control system in accordance with claim 26, furthercomprising: j) increasing the frequency and repeating steps a) throughf), if the desired slope of the fast Fourier transform of the systemresponse does not fall within the slope range.
 31. The control system inaccordance with claim 26, further comprising: a pressure dither system,wherein the pressure of the actuator cylinder during extension andretraction is changed by an incremental amount of pressure (ditherp).32. The control system in accordance with claim 31, wherein the ditherpressure (ditherp) is calculated in accordance with the formula:[((rnd)(maxdither))−((rnd)(maxdither2))], wherein rnd is a random numberfunction between 0 and 1, and maxdither is the pre-selected maximumpressure difference for dither pressure (ditherp).
 33. The controlsystem in accordance with claim 26, further comprising: a frequencyringing system, wherein the location of a particular frequency isreordered among the plurality of actuator cylinders.
 34. The controlsystem in accordance with claim 33, wherein the frequency ringing systemis calculated in accordance with the formula: cylinder i=Mode(i+Mode(C1,6),6)+1, wherein i is the cylinder number, Mode is the remainder of thequotient between any two given numbers, and C1 is the count numberrepresenting a status change in the cylinder frequency location.
 35. Acontrol system for a failure mode testing system having a plurality ofactuator cylinders, each cylinder operating at a pressure and afrequency, wherein the frequency of each of the cylinders is different,wherein the energy level and slope of the fast Fourier transform of thefrequency are capable of changing in response to pressure and frequency,comprising: calculating the change in energy due to pressure (Dep)according to the formula: Dep=((E_(HH)+E_(HL))−(E_(LH)+E_(LL)))/(2dp),wherein E_(HH) is the energy measured during a pressure/frequencycondition corresponding to a high pressure/high frequency condition,E_(HL) is the energy measured during a pressure/frequency conditioncorresponding to a high pressure/low frequency condition, E_(LH) is theenergy measured during a pressure/frequency condition corresponding to alow pressure/high frequency condition, E_(LL) is the energy measuredduring a pressure/frequency condition corresponding to a lowpressure/low frequency condition, and dp is the pre-selected amount bywhich the pressure is either increased or decreased.
 36. A controlsystem for a failure mode testing system having a determinable systemresponse, wherein the testing system includes a plurality of actuatorcylinders, each cylinder operating at a pressure and a frequency,wherein the frequency of each of the cylinders is different, wherein theenergy level and slope of the fast Fourier transform of the systemresponse are capable of changing in response to pressure and frequency,comprising: calculating the change in energy due to frequency (Def)according to the formula: Def=((E_(HH)+E_(LH))−(E_(HL)+E_(LL)))/(2df),wherein E_(HH) is the energy measured during a pressure/frequencycondition corresponding to a pressure/high frequency condition, E_(LH)is the energy measured during a pressure/frequency conditioncorresponding to a low pressure/high frequency condition, E_(HL) is theenergy measured during a pressure/frequency condition corresponding to ahigh pressure/low frequency condition, E_(LL) is the energy measuredduring a pressure/frequency condition corresponding to a lowpressure/low frequency condition, and df is the pre-selected amount bywhich the frequency is either increased or decreased.
 37. A controlsystem for a failure mode testing system having a determinable systemresponse, wherein the testing system includes a plurality of actuatorcylinders, each cylinder operating at a pressure and a frequency,wherein the frequency of each of the cylinders is different, wherein theenergy level and slope of the fast Fourier transform of the systemresponse are capable of changing in response to pressure and frequency,comprising: calculating the change in slope of the fast Fouriertransform of the system response due to pressure (Dsp) according to theformula: Dsp=((m_(HH)+m_(HL))−(m_(LH)+m_(LL)))/(2dp), wherein m_(HH) isthe slope of the fast Fourier transform of the system response measuredduring a pressure/frequency condition corresponding to a highpressure/high frequency condition, m_(HL) is the slope of the fastFourier transform of the system response measured during apressure/frequency condition corresponding to a high pressure/lowfrequency condition, m_(LH) is the slope of the fast Fourier transformof the system response measured during a pressure/frequency conditioncorresponding to a low pressure/high frequency condition, m_(LL) is theslope of the fast Fourier transform of the system response measuredduring a pressure/frequency condition corresponding to a lowpressure/low frequency condition, and dp is the pre-selected amount bywhich the pressure is either increased or decreased.
 38. A controlsystem for a failure mode testing system having a determinable systemresponse, wherein the testing system includes a plurality of actuatorcylinders, each cylinder operating at a pressure and a frequency,wherein the frequency of each of the cylinders is different, wherein theenergy level and slope of the fast Fourier transform of the systemresponse are capable of changing in response to pressure and frequency,comprising: calculating the change in slope of the fast Fouriertransform of the system response due to frequency (Dsf) according to theformula: Dsf=((m_(HH)+m_(LH))−(m_(HL)+m_(LL)))/(2df), wherein m_(HH) isthe slope of the fast Fourier transform of the system response measuredduring a pressure/frequency condition corresponding to a high ispressure/high frequency condition, m_(LH) is the slope of the fastFourier transform of the system response measured during apressure/frequency condition corresponding to a low pressure/highfrequency condition, m_(HL) is the slope of the fast Fourier transformof the system response measured during a pressure/frequency conditioncorresponding to a high pressure/low frequency condition, m_(LL) is theslope of the fast Fourier transform of the system response measuredduring a pressure/frequency condition corresponding to a lowpressure/low frequency condition, and df is the pre-selected amount bywhich the frequency is either increased or decreased.
 39. A controlsystem for a failure mode testing system having a determinable systemresponse, wherein the testing system includes a plurality of actuatorcylinders, each cylinder operating at a pressure and a frequency,wherein the frequency of each of the cylinders is different, wherein theenergy level and slope of the fast Fourier transform of the systemresponse are capable of changing in response to pressure and frequency,comprising: calculating the average energy (E1) according to thefollowing formula: E1=average (E_(HH), E_(HL), E_(LH), E_(LL)), whereinEHH is the energy measured during a pressure/frequency conditioncorresponding to a high pressure/high frequency condition, E_(HL) is theenergy measured during a pressure/frequency condition corresponding to ahigh pressure/low frequency condition, E_(LH) is the energy measuredduring a pressure/frequency condition corresponding to a lowpressure/high frequency condition, and E_(LL) is the energy measuredduring a pressure/frequency condition corresponding to a lowpressure/low frequency condition.
 40. A control system for a failuremode testing system having a determinable system response, wherein thetesting system includes a plurality of actuator cylinders, each cylinderoperating at a pressure and a frequency, wherein the frequency of eachof the cylinders is different, wherein the energy level and slope of thefast Fourier transform of the system response are capable of changing inresponse to pressure and frequency, comprising: calculating the newtarget energy (E2) according to the following formula:E2=E1+(E_(DESIRED)−E1)/n, wherein E1 is the average energy, E_(DESIRED)is the desired energy level of the system response, and n is a numbergreater than
 1. 41. A control system for a failure mode testing systemhaving a determinable system response, wherein the testing systemincludes a plurality of actuator cylinders, each cylinder operating at apressure and a frequency, wherein the frequency of each of the cylindersis different, wherein the energy level and slope of the fast Fouriertransform of the system response are capable of changing in response topressure and frequency, comprising: calculating the average slope of thefast Fourier transform of the system response (S1) according to thefollowing formula: S1=average (m_(HH), m_(HL), m_(LH), m_(LL)), whereinm_(HH) is the slope of the fast Fourier transform of the system responsemeasured during a pressure/frequency condition corresponding to a highpressure/high frequency condition, m_(HL) is the slope of the fastFourier transform of the system response measured during apressure/frequency condition corresponding to a high pressure/lowfrequency condition, m_(LH) is the slope of the fast Fourier transformof the system response measured during a pressure/frequency conditioncorresponding to a low pressure/high frequency condition, and m_(LL) isthe slope of the fast Fourier transform of the system response measuredduring a pressure/frequency condition corresponding to a lowpressure/low frequency condition.
 42. A control system for a failuremode testing system having a determinable system response, wherein thetesting system includes a plurality of actuator cylinders, each cylinderoperating at a pressure and a frequency, wherein the frequency of eachof the cylinders is different, wherein the energy level and slope of thefast Fourier transform of the system response are capable of changing inresponse to pressure and frequency, comprising: calculating the newtarget slope of the fast Fourier transform of the system response (S2)according to the following formula: S2=S1+(S_(DESIRED)−S1)/n, wherein S1is the average slope of the fast Fourier transform of the systemresponse, S_(DESIRED) is the desired slope of the fast Fourier transformof the system response, and n is a number greater than
 1. 43. A controlsystem for a failure mode testing system having a determinable systemresponse, wherein the testing system includes a plurality of actuatorcylinders, each cylinder operating at a pressure and a frequency,wherein the frequency of each of the cylinders is different, wherein theenergy level and slope of the fast Fourier transform of the systemresponse are capable of changing in response to pressure and frequency,comprising: calculating the new target pressure (P_(NEW)) according tothe formula:P_(NEW)=[(DsfE2−DsfE1−DefS2+DefS1−DepDsfP)/(DefDsp−DepDsf)], wherein Defis the change in energy due to frequency, Dep is the change in energydue to pressure, Dsf is the change in slope of the fast Fouriertransform of the system response due to frequency, Dsp is the change inslope of the fast Fourier transform of the system response due topressure, E1 is the average energy, E2 is the new target energy, S1 isthe average slope of the fast Fourier transform of the system response,and S2 is the new target slope of the fast Fourier transform of thesystem response.
 44. A control system for a failure mode testing systemhaving a determinable system response, wherein the testing systemincludes a plurality of actuator cylinders, each cylinder operating at apressure and a frequency, wherein the frequency of each of the cylindersis different, wherein the energy level and slope of the fast Fouriertransform of the system response are capable of changing in response topressure and frequency, comprising: calculating the new target frequency(F_(NEW)) according to the formula:F_(NEW)=[(DspE2−DspE1−DepS2+DepS1−DepDsfF)/(DefDsp−DepDsf)], wherein Defis the change in energy due to frequency, Dep is the change in energydue to pressure, Dsf is the change in slope of the fast Fouriertransform of the system response due to frequency, Dsp is the change inslope of the fast Fourier transform of the system response due topressure, E1 is the average energy, E2 is the new target energy, S1 isthe average slope of the fast Fourier transform of the system response,and S2 is the new target slope of the fast Fourier transform of thesystem response.
 45. A control system for a failure mode testing systemhaving a plurality of actuator cylinders, each cylinder operating at aninitial pressure and an initial frequency, wherein the frequency of eachof the cylinders is different, comprising: a pressure dither system,wherein the pressure of the actuator cylinder during extension andretraction is changed by an incremental amount of pressure (ditherp).46. The control system in accordance with claim 45, wherein the ditherpressure (ditherp) is calculated in accordance with the formula:[((rnd)(maxdither))−((rnd)(maxdither2))], wherein rnd is a random numberfunction between 0 and 1, and maxdither is the pre-selected maximumpressure difference for dither pressure (ditherp).
 47. A control systemfor a failure mode testing system having a plurality of actuatorcylinders, each cylinder operating at an initial pressure and an initialfrequency, wherein the frequency of each of the cylinders is different,comprising: a frequency ringing system, wherein the location of aparticular frequency is randomly reordered among the plurality ofactuator cylinders.
 48. The control system in accordance with claim 47,wherein the frequency ringing system is calculated in accordance withthe formula: cylinder i=Mode(i+Mode(C1, 6),6)+1, wherein i is thecylinder number, Mode is the remainder of the quotient between any twogiven numbers, and C1 is the count number representing a status changein the cylinder frequency location.
 49. A control system for a failuremode testing system having a determinable system response, wherein thetesting system includes a plurality of actuator cylinders, each cylinderoperating at an initial pressure and an initial frequency, wherein thefrequency of each of the cylinders is different, comprising: a)selecting a desired system response; b) changing an operationalparameter of the cylinders by a pre-selected amount in order to create afirst pressure/frequency condition, wherein the operational parameter isselected from the group consisting of pressure, frequency, andcombinations thereof; and c) determining the system response under thefirst pressure/frequency condition.
 50. The control system in accordancewith claim 49, further comprising: d) storing the system responsedetermination of the first pressure/frequency condition in a datastorage medium.
 51. The control system in accordance with claim 50,further comprising: e) changing an operational parameter of thecylinders by a pre-selected amount in order to create a secondpressure/frequency condition different from the first pressure/frequencycondition; and f) determining the system response under the secondpressure/frequency condition.
 52. The control system in accordance withclaim 51, further comprising: g) storing the system responsedetermination of the second pressure/frequency condition in a datastorage medium.
 53. The control system in accordance with claim 52,further comprising: h) changing an operational parameter of thecylinders by a pre-selected amount in order to create a thirdpressure/frequency condition different from the first and secondpressure/frequency conditions; and i) determining the system responseunder the third pressure/frequency condition.
 54. The control system inaccordance with claim 53, further comprising: j) storing the systemresponse determination of the third pressure/frequency condition in adata storage medium.
 55. The control system in accordance with claim 54,further comprising: k) changing an operational parameter of thecylinders by a pre-selected amount in order to create a fourthpressure/frequency condition different from the first, second, and thirdpressure/frequency conditions; and l) determining the system responseunder the fourth pressure/frequency condition.
 56. The control system inaccordance with claim 55, further comprising: m) storing the systemresponse determination of the fourth pressure/frequency condition in adata storage medium.
 57. The control system in accordance with claim 56,further comprising: n) determining whether the desired system responseis present.
 58. The control system in accordance with claim 57, furthercomprising: o) decreasing the pre-selected amount that the operationalparameter is changed by and repeating steps b) through n), until thedesired system response is present.
 59. The control system in accordancewith claim 57, further comprising: p) increasing the pre-selected amountthat the operational parameter is increased by and repeating steps b)through n), until the desired system response is present.
 60. Thecontrol system in accordance with claim 49, further comprising: apressure dither system, wherein the pressure of the actuator cylinderduring extension and retraction is changed by an incremental amount ofpressure (ditherp).
 61. The control system in accordance with claim 60,wherein the dither pressure (ditherp) is calculated in accordance withthe formula: [((rnd)(maxdither))−((rnd)(maxdither2))], wherein rnd is arandom number function between 0 and 1, and maxdither is thepre-selected maximum pressure difference for dither pressure (ditherp).62. The control system in accordance with claim 49, further comprising:a frequency ringing system, wherein the location of a particularfrequency is reordered among the plurality of actuator cylinders. 63.The control system in accordance with claim 62, wherein the frequencyringing system is calculated in accordance with the formula: cylinderi=Mode(i+Mode(C1, 6),6)+1, wherein i is the cylinder number, Mode is theremainder of the quotient between any two given numbers, and C1 is thecount number representing a status change in the cylinder frequencylocation.
 64. A control system for a failure mode testing system havinga determinable system response, wherein the testing system includes aplurality of actuator cylinders, each cylinder operating at an initialpressure and an initial frequency, wherein the frequency of each of thecylinders is different, comprising: a) selecting a desired systemresponse; b) determining the system response; c) determining whether thedesired system response is present; and d) changing an operationalparameter of the cylinders by a sufficient amount in order to achievethe desired system response, wherein the operational parameter isselected from the group consisting of pressure, frequency, andcombinations thereof.
 65. The control system in accordance with claim64, further comprising: e) decreasing the amount that the operationalparameter is changed by and repeating steps b) through c), until thedesired system response is present.
 66. The control system in accordancewith claim 64, further comprising: f) increasing the amount that theoperational parameter is increased by and repeating steps b) through c),until the desired system response is present.
 67. The control system inaccordance with claim 64, further comprising: a pressure dither system,wherein the pressure of the actuator cylinder during extension andretraction is changed by an incremental amount of pressure (ditherp).68. The control system in accordance with claim 64, wherein the ditherpressure (ditherp) is calculated in accordance with the formula:[((rnd)(maxdither))−((rnd)(maxdither2))], wherein rnd is a random numberfunction between 0 and 1, and maxdither is the pre-selected maximumpressure difference for dither pressure (ditherp).
 69. The controlsystem in accordance with claim 64, further comprising: a frequencyringing system, wherein the location of a particular frequency isreordered among the plurality of actuator cylinders.
 70. The controlsystem in accordance with claim 69, wherein the frequency ringing systemis calculated in accordance with the formula: cylinder i=Mode(i+Mode(C1,6),6)+1, wherein i is the cylinder number, Mode is the remainder of thequotient between any two given numbers, and C1 is the count numberrepresenting a status change in the cylinder frequency location.